1. Field of the Invention
The present invention relates generally to a sheet separator, and more particularly, to a document sheet separator adapted for use in an optical document reader.
2. Description of the Related Art
Generally, an optical document reader is an apparatus in which documents are sent or fed one sheet at a time from the top of a stack of document sheets set in the hopper of the optical document reader to an optical document reader unit that optically reads information printed on the document. Typically, such optical document readers include a document separator for separating sheets of documents into single sheets whenever two sheets are fed from the hopper at the same time, that is, whenever a double-feed occurs. Obviously, such a double-feed is undesirable and should be avoided wherever possible.
At present the range of types of materials from which documents are made is very large. In some cases, these materials from which documents are made are such that single sheets of such documents tend to stick together, making a double-feed more likely to occur. As a result, a sheet separator with an improved ability to separate such double-fed sheets of documents into single sheets is needed.
FIGS. 1A and 1B show an example of the prior art, that is, a conventional sheet separator. As shown in FIGS. 1A and 1B, the conventional sheet separator 10A consists of one separating roller 11, one torque roller 12, a pulse motor 13 that rotates the separating roller 11 and a separation force application mechanism 14 that imparts a separation force F to the torque roller 12, with the torque roller 12 being pressed against the separating roller 11. The torque roller 12 is coupled to a torque limiter not shown in the diagram so that the torque roller 12 remains stopped even if a certain amount of torque is applied and begins to rotate only when a predetermined amount of torque is applied. The separation force application mechanism 14 can be used to adjust the separation force F.
The above-described conventional sheet separator 10 typically remains inactive unless a double-feed occurs, that is, when the first document sheet 21-1 is fed onward by a pick-up roller 22 and a second document sheet 21-2 sticks to the back of a first document sheet 21-1 and is dragged together with the first document sheet 21-1, the first sheet 21-1 being the sheet positioned at the top of a stack 21 of multiple document sheets set in a hopper 20.
In the event of a double-feed like that described above, a forward longitudinal edge of the second sheet 21-2, which is on the bottom, is braked by the stopped torque roller 12 and the forward advance of the second sheet 21-2 is retarded thereby. At the same time, the first sheet 21-1, which is on the top and against which a feed force is exerted by the separating roller 11, slides over and separates from the second sheet 21-2 so that only the first sheet 21-1 is fed onward to the feed roller 23 by the separating roller 11. After the first sheet 21-1 is fed onward the second sheet, which had been braked by the torque roller 12 and any forward progress retarded thereby, is fed onward by the separating roller 11, with the torque roller 12 being rotated by the force of frictional contact with the second sheet 21-2.
It should be noted that, for clarity of illustration only, in FIG. 1B the second sheet 21-2 on the bottom is shown slightly smaller than the first sheet 21-1 on the top. A similar approach is taken with respect to FIGS. 7B, 8C and 8E.
However, a problem arises with the conventional sheet separator 10 like that described above insofar as the conventional sheet separator 10 is not fully capable of separating double-fed sheets. As a result, when the coefficient of friction between sheets is large, that is, when it is hard to separate the sheets set in the hopper 20, double-fed sheets are not separated but might pass through the document sheet separator 10 in that double-fed state.
Typically, the coefficient of friction between two documents stuck together differs depending on the type of documents in question, so the separation force application mechanism 14 described above is used to adjust the separation force F downward, that is, to reduce the separation force F in order to make it easier to separate the sheets. However, even with this adjustment of the separation force F depending on the type of paper used to make the document sheets it sometimes happens that document sheets are double-fed through the sheet separator 10.
Accordingly, it is an object of the present invention to provide an improved and useful document sheet separator in which the above-described disadvantage is eliminated.
The above-described object of the present invention is achieved by a sheet separator that separates sheets of documents supplied as a stack into single sheets, the sheet separator comprising:
a first separating mechanism having a first separating roller; and
a second separating mechanism having second separating rollers,
the second separating mechanism provided at a position downstream from a position of the first separating mechanism.
According to the invention described above, the second separating mechanism separates those sheets that are fed onward without being separated by the first separating mechanism.
Additionally, the above-described object of the present invention is also achieved by the sheet separator as described above, wherein a peripheral velocity of the second separating rollers is set lower than a peripheral velocity of the first separating roller.
According to the invention described above, setting the peripheral speed of the second separating rollers slower than the peripheral speed of the first separating roller causes a compressive force to act on the top sheet of two sheets double-fed onward without being separated by the first separating mechanism, causing such a top sheet to form an upward bulge.
Additionally, the above-described object of the present invention is also achieved by the sheet separator as described above, wherein the first separating roller is positioned so as to act upon a central portion in a lateral direction of a sheet transported thereto and the second separating rollers are positioned so as to act upon edge surface portions in the lateral direction of the sheet transported thereto.
According to the invention described above, positioning the second separating rollers so as to act upon edge portions of the sheet transported thereto causes the separation force to act on locations near the corners of the top sheet of two double-fed sheets, at which locations the top sheet is more easily separated from the bottom sheet.
Additionally, the above-described object of the present invention is also achieved by the sheet separator as described above, wherein:
a peripheral velocity of the second separating roller is set lower than a peripheral velocity of the first separating roller;
the first separating roller is positioned so as to act upon a central portion in a lateral direction of a sheet transported thereto; and
the second separating rollers are positioned so as to act upon edge surface portions in the lateral direction of the sheet transported thereto.
According to the invention described above, setting the peripheral speed of the second separating rollers slower than the peripheral speed of the first separating roller causes a compressive force to act on a portion of the top sheet of two sheets double-fed onward without being separated by the first separating mechanism that lies between the first separating roller and the second separating rollers, causing such a top sheet to form an upward bulge.
Additionally, as described above, positioning the second separating rollers so as to act upon edge portions of the sheet transported thereto causes the separation force to act on locations near the corners of the top sheet of two double-fed sheets, at which locations the top sheet is more easily separated from the bottom sheet.
Additionally, positioning the first separating roller so as to act upon a central portion of a sheet transported thereto causes the separation force applied by the second separating rollers to become a twisting force with respect to the location at which the first separating roller exerts a separation force.
Additionally, the above-described object of the present invention is also achieved by the sheet separator as described above, wherein the second separating rollers are supported so that positions of the second separating rollers in a lateral direction of a sheet transported thereto can be changed.
According to the invention described above, the document sheet separator according to the present invention can accommodate a plurality of different sizes of paper.
Additionally, the above-described object of the present invention is also achieved by the sheet separator as described above, wherein a distance between the first separating mechanism and the second separating mechanism is shorter than a longitudinal length of the sheet.
Additionally, the above-described object of the present invention is also achieved by an optical document reader comprising:
a hopper, to which a plurality of sheets can be set;
a sheet separator that separates sheets of documents supplied as a stack into single sheets;
a feed roller that transports documents;
an optical document reading unit that optically reads data inscribed on the documents; and
a stacker that stacks and outputs documents from which data has been optically read by the optical document reading unit, the sheet separator comprising:
a first separating mechanism having a first separating roller; and
a second separating mechanism having second separating rollers,
the second separating mechanism provided at a position downstream from a position of the first separating mechanism.
According to the invention described above a double-feed is less likely to occur and, accordingly, a more reliable optical document reader can be attained.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.